Actuator unit for motor vehicle brakes

ABSTRACT

A front housing part (20) of a brake pressure booster (12) carries two hollow inner threaded members (26) which each engage in a hole (68) formed in a flange (70) of a master cylinder (14) and each support the head (52) of a bolt (50). Each one of the bolts (50) extends through the associated inner threaded member (26) and through the booster (12) and has a threaded portion (56) which projects rearwardly out of the booster to be screwed into a threaded sleeve (18) at a dividing wall (16) of a motor vehicle. The flange (70) of the master cylinder (14) is clamped between the inner threaded members (26) and outer threaded members (60) which likewise are hollow and have inner diameters greater than the head (52) of the corresponding bolt (50). The outer threaded members (60) each include a sleeve-like extension (62) engaging in the corresponding hole (68) of the flange (70) and being screw connected to the inner threaded member (26) received in said hole.

The invention relates to an actuator unit for motor vehicle brakes,comprising

a brake pressure booster which comprises front and rear housing partsand includes at least one movable partition at which differentialpressure can be generated,

a master cylinder which includes a flange fastened to the front housingpart and having at least one through hole, and

at least one bolt which comprises a shaft extending through the hole inthe flange and through the two housing parts as well as the movablepartition of the booster, a head disposed in front of the front housingpart, and a threaded portion projecting out of the rear housing part andadapted to be screwed into a stationary thread presented in a dividingwall of a motor vehicle.

Such an actuator unit is known from EP 0 119 880 A1. Two bolts havetheir shafts extending through a hole each in a flange of the mastercylinder and through one each of two tubes which are disposed within thebrake pressure booster in parallel with the axis thereof and which arefixed to the rear housing part and guided for axial displacement at thefront housing part. By means of these bolts, the master cylindertogether with the booster can be fastened from the engine compartment ofa motor vehicle to the dashboard thereof at which nuts are mounted forthis purpose. This means that no manipulations to fix the mastercylinder and the booster need be done in the passenger compartment.Where the master cylinder and booster are held together in this mannerand both attached to the dashboard, it is not possible to separate themaster cylinder from the booster without first disassembling the latterfrom the dashboard. Another actuator unit for motor vehicle brakes withwhich a master cylinder and a brake pressure booster are to be fastenedjointly to the dashboard of a motor vehicle by means of a pair ofthreaded bolts is known from DE 28 30 262 C2. The threaded bolts extendparaxially through the booster and each include front and rear threadedportions which can be passed through the dashboard and secured by a nuteach from the passenger compartment. Apart from manipulations from theengine compartment to secure the booster at the dashboard of a motorvehicle, further manipulations thus are required which can beaccomplished only in the passenger compartment. Two hollow bolts arefastened to the front housing part of the booster, each extendingthrough a hole in a flange of the master cylinder. The threaded boltspass through one each of these hollow bolts. A small nut is screwed ontothe front threaded portion of each threaded bolt so as to press againstthe front face of the corresponding hollow bolt. A larger nut each isscrewed onto the two hollow bolts to press from the front against theflange of the master cylinder. The inner diameter of the larger nuts isgreater than the greatest outer diameter of the small nuts. Consequentlythe master cylinder can be disassembled from the booster withoutremoving the booster from the dashboard. That is done by unscrewing thelarger nuts from the hollow bolts and withdrawing them to the frontwhile passing them over the small nuts. Subsequently, also the flange ofthe master cylinder can be pulled off over the small nuts withoutloosening the latter. The structural length in axial direction of thisknown arrangement for fastening the brake pressure booster and themaster cylinder is quite considerable and, therefore, it is difficult tofind room for it when a brake fluid reservoir and the like are attachedin the usual manner to the master cylinder. It is the object of theinvention to improve an actuator unit for motor vehicle brakes, composedsubstantially of a brake pressure booster and a master cylinder, in sucha way that space saving fastening elements are sufficient to hold themaster cylinder and booster together, to fasten the unit as a whole to adividing wall, especially the dashboard of a motor vehicle, from theengine compartment of the same without any manipulations from thepassenger compartment, and furthermore to permit subsequent replacementof the master cylinder without having to disassemble the booster fromthe dividing wall of the motor vehicle.

The object is met, in accordance with the invention, by the features ofclaim 1. Advantageous further developments of the invention arepresented in the subclaims.

Embodiments of the invention will be described in greater detail belowwith reference to diagrammatic drawings, in which:

FIGS. 1 to 3 illustrate three embodiments of actuator units according tothe invention for motor vehicle brakes, each in axial longitudinalsection.

The actuator unit 10 shown in FIG. 1 essentially consists of a pneumaticbrake pressure booster 12 in conventional tandem arrangement with anhydraulic master cylinder 14 likewise of conventional structure for adual circuit brake system. The booster 12 and master cylinder 14 arealigned along an axis A and designed such that the actuator unit 10 as awhole can be mounted on a dividing wall 16, especially the dashboard ofa motor vehicle, the wall being provided for this purpose with threadedsleeves 18 or the like.

The brake pressure booster 12 comprises front, central, and rear housingparts 20, 22, and 24, respectively, made in the usual way by deepdrawing relatively thin sheet steel. A pair of sleeve-like innerthreaded members 26 are tightly secured to the front housing part 20,such as by flanging, with a sealing ring positioned in between, ifdesired. In similar fashion, a pair of sleeve-like rear threaded members28 are tightly secured to the rear housing part 24. Each one of theinner threaded members 26 is connected by a stiff tube 30 to thecorresponding one of the rear threaded members 28, the tube beingthreaded tightly into an inner thread formed in the rear threaded member28 and also being tightly secured to the front threaded member 26, suchas by welding.

A movable front partition 32, a stationary central partition 33, and amovable rear partition 34 subdivide the interior of the booster 12 intofour chambers 40, 42, 44, and 46, while elastic bellows 36 and 38 sealthe movable front partition 32 and the movable rear partition 34,respectively, with respect to the tubes 30. Chambers 40 and 44 are inconstant communication with each other through a central area of thebooster 12 and, furthermore, connected in the usual way (not shown) to avacuum source, for example, a suction manifold of an internal combustionengine. Also chambers 42 and 46 are connected with each other at alltimes through the elastic bellows 38, as is customary with brakepressure boosters in tandem arrangement.

A control valve unit 48, likewise of conventional structure, is arrangedin the rear zone of the booster 12 to make sure that, in the inoperativecondition, the pressure between all the chambers is balanced, whereas,upon operation, the two chambers 40 and 44 will be separated from thetwo chambers 42 and 46, such that ambient air flow is admitted into thelatter, whereby a pressure difference is created at the two movablepartitions 32 and 34, generating forwardly directed forces to actuatethe master cylinder 14.

A bolt 50 having a head 52, a cylindrical shaft 54, and a rear portion56 formed with an external thread to be screwed into a respective one ofthe threaded sleeves 18 is pushed from the front to the rear througheach of the inner threaded members 26, the tube 30 contiguous to thesame, and the corresponding rear threaded member 28. The head 52--FIG. 1shows it to be a cylindrical head with a hexagonal recess--rests againstthe front face 58 of the corresponding inner threaded member 26. As soonas the bolts 50 are tightened, i.e. as their rear threaded portions 56are screwed firmly into the respective threaded sleeve 18 at thedividing wall 16 of the motor vehicle, whereby the shaft 54 is subjectedto tensile stress, corresponding compressive stress prevails in thecorresponding tube 30. This is so, regardless of whether the mastercylinder 14 is mounted on the dividing wall 16 together with the booster12 or alone at a later stage, and it is also the case when the mastercylinder 14 is exchanged, for instance, because of some damagediscovered subsequently.

The actuator unit 10 normally is a unit ready to be installed as a wholein a motor vehicle and, therefore, the master cylinder 14 first isassembled with the brake pressure booster 12. For this reason an outerthreaded member 60 each is associated with each of the two sleeve-likeinner threaded members 26. The outer threaded member comprises asleeve-like cylindrical extension 62, a shoulder 64, and a hexgonal end66 or similar feature to be engaged by a torque transmitting tool. Byits respective cylindrical extension 60 each of the two outer threadedmembers 60 engages in a through hole 68 provided in a flange 70 formedat the master cylinder 14 and is threaded upon the associated innerthreaded member 26 until the shoulder 64 firmly abuts against the flange70. Hereby the flange 70 is clamped against the upper housing part 20.The inner threaded members 26 back up the sheet of the front housingpart 20, pressing it against the backside of the flange 70 so that theotherwise customary reinforcing inlay in the front housing part 20 canbe dispensed with.

In the case of the embodiment illustrated in FIG. 1 the bolts 50 can bepushed into the tubes 30 either before or after assembly of the booster12 with the master cylinder 14. In any case, they remain in position ifthe master cylinder 14 needs to be exchanged upon mounting of theactuator unit 10 on the dividing wall 16. The inner diameter of theouter threaded members 60 is slightly bigger than the outer diameter ofthe head 52 of the corresponding bolt 50. For this reason each one ofthe outer threaded members 60 can be unscrewed from the correspondinginner threaded member 26 and pulled off over the head 52 of therespective bolt 50, thus releasing the flange 70 so that also the mastercylinder 14 can be pulled off.

The actuator unit 10 according to FIG. 2 differs from the one shown inFIG. 1 above all in that the tubes 30 are left out and the bolts 50 havetaken over their function as spacers. To this end, a cover 72 is screwedinto each of the outer threaded members 60 in such manner that the head52 of the respective bolt 50 is firmly clamped between this cover andthe front face 58 of the inner threaded member 26. Furthermore, eachbolt 50 is formed with a rear stop 74 to be engaged by a support ring 76which is fastened to the rear housing part 24 and through which extendsthe rear portion 56 of the bolt 50. According to FIG. 2, the rear stop74 is an adjustment nut screwed on the rear portion 56 and locked inplace, for instance, by calking or a retaining varnish once theadjustment has been accomplished.

The bolts 50 are prevented from slipping to the front out of the supportrings 76 before the cover 72 is mounted in that they each carry alocking element 78 on their shafts 54. In the case of FIG. 2 this isembodied by a sleeve which is slipped on the shaft and will abut againstthe bellows 36 upon limited forward displacement of the correspondingbolt.

According to FIG. 3, each of the bolts 50 can be formed integrally witha rear stop 74. If adjustment should be required a more or less thicksealing ring could be positioned between the stop 74 and thecorresponding support ring 76. In any case, it is important that each ofthe rear stops 74 acts sealingly against the corresponding support ring76. That is why it is convenient to dispose a sealing ring in between.As shown in FIG. 3, each bolt 50 also is formed integrally with itsrespective locking element 78.

What is claimed is:
 1. An actuator unit (10) for motor vehicle brakes,comprisinga brake pressure booster (12) which comprises front and rearhousing parts (20, 24) and includes at least one movable partition (32,34) at which differential pressure can be generated, a master cylinder(14) which includes a flange (70) fastened to the front housing part(20) and having at least one through hole (68), and at least one bolt(50) which comprises a shaft (54) extending through the hole (68) in theflange (70) and through the two housing parts (20, 24) as well as themovable partition (32, 34) of the booster (12), a head (52) disposed infront of the front housing part (20), and a threaded portion (56)projecting out of the rear housing part (24) and adapted to be screwedinto a stationary thread presented in a dividing wall (16) of a motorvehicle, characterized in that a hollow, inner threaded member (26)having a front face (58) is fastened to the front housing part (20), theshaft (54) of the bolt (50) passes through the inner threaded member(26) and the head (52) of the bolt rests on the front face (58) thereof,the flange (70) is clamped between the inner threaded member (26) and ahollow, outer threaded member (60) whose inner diameter is greater thanthe outer diameter of the head (52) of the bolt (50), and the outerthreaded member (60) includes a sleeve-like extension (62) which engagesin the hole (68) formed in the flange (70) and is screw connected to theinner threaded member (26).
 2. The actuator unit as claimed in claim 1,characterized in that the head (52) of the bolt (50) is disposed atleast partly within the outer threaded member (26).
 3. The actuator unitas claimed in claim 2, characterized in that the head (52) of the bolt(50) is clamped between the inner threaded member (26) and a cover (72)which is screw connected to the outer threaded member (60).
 4. Theactuator unit as claimed in claim 3, characterized in that the bolt (50)includes a rear stop (74) by which it rests on the rear housing part(24).
 5. The actuator unit as claimed in claim 4, characterized in thatthe rear stop (74) is screwed like a nut on the rear portion (56) of thebolt (50) and is disposed inside the booster (12) and locked againstrotation.
 6. The actuator unit as claimed in any one of claims 3 to 5,characterized in that the bolt (50) is connected to a retention element(78) which is arranged inside the booster (12) and prevents the boltfrom falling out to the front prior to being threaded into the dividingwall (16) of the motor vehicle.
 7. The actuator unit as claimed in claim1 or 2, characterized in that the bolt (50) extends through a tube (30)disposed within the booster (12) and maintaining a predetermineddistance between the front and rear housing parts (20, 24).
 8. Theactuator as claimed in claim 7, characterized in that the tube (30) isscrew connected to a rear threaded member (28) which is fastened to therear housing part (24).